1. Field of the Invention
The present invention relates, in general, to an apparatus for actuating valves in vehicles in a variable valve control manner that hydraulically controls the valves with respect to the timing and lift on opening of the valves.
2. Description of Related Art
Generally, engines have predetermined valve opening/closing timing that is able to produce maximum output at specified revolutions per minute (RPM). That is, engines need a slow valve opening/closing timing at a low RPM in order to perform expansion and explosion of a fuel-air mixture, and engines need a rapid valve opening/closing timing at a high RPM in order to perform exhaust of the exploded fuel-air mixture. However, if the timing is set to the low or high RPM mode at high or low RPM, respectively, the exhaust or compression, respectively, of the fuel-air mixture is delayed, resulting in a considerable reduction in performance of engines.
In order to solve these problems, a variable valve timing technology has been developed, which alters the opening/closing timing of intake or exhaust valves depending upon the RPM of an engine, thereby obtaining high fuel-efficiency and output at both low and high RPMs. The technology has three types of operation: altering only the timing of valve opening/closing; altering both the timing and lift of valve opening/closing; and altering only the lift of valve opening/closing.
However, generally, in order to control the timing and lift of valve opening/closing, high-pressure hydraulic systems should be provided for each cylinder, which thus increases the manufacturing cost and weight of a product. Further, due to a pressure differential occurring between cylinders, there is also a difference in lift of valve opening/closing for each cylinder, and all of the cylinders generate high hydraulic pressure, thereby resulting in an occurrence of power loss owing to the generation of high pressure, and therefore deteriorating fuel efficiency.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.